Optical slicer for improving the spectral resolution of a dispersive spectrograph

ABSTRACT

An optical slicer for generating an output spot comprising an image compressor which receives a substantially collimated input beam and compresses the beam, wherein the input beam, if passed through a focusing lens, produces an input spot; an image reformatter which receives the compressed beam to reformat the beam into a plurality of sliced portions of the compressed beam and vertically stacks the portions substantially parallel to each other; and an image expander which expands the reformatted beam to produce a collimated output beam which, if passed through the focusing lens, produces the output spot that is expanded in a first dimension and compressed in a second dimension relative to the input spot.

RELATED APPLICATIONS

This application claims priority from U.S. Provisional Application No.61/247,762 filed Oct. 1, 2009 and U.S. Provisional Application No.61/350,264 filed Jun. 1, 2010, the contents of each of which are hereinincorporated by reference.

FIELD OF INVENTION

This invention relates to the field of spectroscopy and morespecifically relates to improved apparatus and methods for improvingspectral resolution.

BACKGROUND

A typical optical spectrograph includes a small input aperture,typically a slit, however, can alternatively be a circular pinhole or anoptical fiber; however, for the sake of brevity, will hereinafter bereferred to as a slit. A converging cone of light, is projected towardsthe slit and a portion of the light passes through the slit. In atypical optical spectrograph, this slit of light is projected onto alens which collimates the slit of light to form a beam of parallel lightrays. In a typical optical spectrograph, a dispersive element, such as,a prism, a transmission grating, or reflection grating, bends thecollimated beams by differing amounts, depending on the wavelength ofthe light. Typically, a camera lens brings these bent collimated beamsinto focus onto an array detector, such as, a charged-coupled device(CCD) detector located at the final focal plane, and which may recordthe light intensities of the various wavelengths.

In a typical optical spectrograph, the collimating lens and the cameralens act as an image relay, to create images of the light passingthrough the slit on the detector, such as a CCD detector, which may bedisplaced laterally depending on the wavelength of the light. Theresolution of an optical spectrograph, i.e., its ability to detect andmeasure narrow spectral features such as absorption or emission lines,can be dependent upon various characteristics. Such characteristics mayinclude the dispersing element, such as, the prism, transmissiongrating, or reflection grating; the focal length of the camera lens; andthe width of the slit. For a particular disperser and camera lens, theresolution of the spectrograph can be increased by narrowing the widthof the input slit, which causes each image of the light passing throughthe slit (depending on the wavelength of the light) and onto a detector,subtending a smaller section of the detector, allowing adjacent spectralelements to be more easily distinguished from each other.

By narrowing the width of the input slit, less light passestherethrough, which can reduce the quality of any measurements due to areduction in the signal-to-noise ratio. In some applications, such asastronomical spectroscopy, high-speed biomedical spectroscopy,high-resolution spectroscopy, or Raman spectroscopy, this loss ofefficiency can be a limiting factor in the performance of the opticalspectrograph. A device which increases the amount of light that can passthrough the slit by horizontally compressing and vertically expanding aspot image of an input beam of light, producing a slit, whilesubstantially maintaining light intensity or flux density, would beadvantageous in the field of optical spectrography.

A person of skill will understand that the terms horizontal, verticaland other such terms used throughout this description, such as, aboveand below, are used for the sake of explaining various embodiments ofthe invention, and that such terms are not intended to be limiting ofthe present invention.

Optical slicers can be useful to receive an input beam and produceoutput beams for generating slits. The use of transparent prisms andplates to slice an input beam can produce a slit that is tilted alongthe optical axis, and additionally the slicing of an optical beam canoccur along the hypotenuse of a 45° prism, which can result in focalpoint degradation due to different sections of the sliced image beinglocated at different focal positions. The performance of such slicerscan depend on the absorption coefficient and index of refraction of theprism used (both wavelength dependent). These deficiencies can limit theuse of such slicers as broadband devices.

Other slicers, such as pupil slicers, possess drawbacks such as theinability to obtain high-resolution spectral information from differentportions of an image. Additionally, such slicers can be large in size,and can result in reduced or inefficient implementation with a varietyof systems. Current slicers that employ a glass-based design tend to usea Lagrange-constant transformer to bring light from a Raman opticalsource to an optical spectrometer. The transformer involves eightdifferent cylindrical and spherical lenses, as well as two stacks of tenprecisely positioned cylindrical lenses. The resulting device can have alength of more than 58 inches along the main optical axis, a size atwhich it tends to be both difficult to maintain alignment, and difficultto maneuver or employ in any setting outside of a tightly-controlledlaboratory.

In some pupil slicers, two slit images can be generated on differentportions of a CCD detector. This implementation can present thedisadvantage that the slit images are spaced on the detector with gapsin between, which can add noise to the signal, decreasing the quality ofthe output data. Additionally, in such slicers, the gaps can wastevaluable detector area, limiting the number of spectra (or spectralorders) that can be fit upon the detector. Further, when using suchslicers, the detector readout may not be optimal due to the spectrumbeing spread over the detector area.

Slicers using optical fiber bundles to allow the extended (often round)image of an input source to be formed into a narrow slit can cause thedegradation of the output ratio to be large and the total performance tobe inefficient. Existing slicer devices uniformly suffer this decreasedefficiency and output ratio, representing a clearly-defined objective ofslicer design and implementation.

SUMMARY OF THE INVENTION

In an aspect of the present invention there is provided an opticalslicer for generating an output spot comprising an image compressorwhich receives a substantially collimated input beam and compresses thebeam, wherein the input beam, if passed through a focusing lens,produces an input spot; an image reformatter which receives thecompressed beam to reformat the beam into a plurality of sliced portionsof the compressed beam and vertically stacks the portions substantiallyparallel to each other; and an image expander which expands thereformatted beam to produce a collimated output beam which, if passedthrough the focusing lens, produces an output spot that is expanded in afirst dimension, and compressed in a second dimension, relative to theinput spot.

In some embodiments of the present invention, the compressed beam may becompressed vertically and be substantially similar horizontally relativeto the input beam and the output beam may be expanded horizontallyrelative to the reformatted beam and may have substantially similardimensions to the input beam.

In other embodiments, the optical slicer may have a slicing factor, n.The number of sliced portions of the compressed beam may be equal to nand the output beam may be expanded vertically by the factor n andcompressed horizontally by the factor n, relative to the input spot.

The compressor may have a convex lens and a concave lens, wherein theconvex lens may receive the input beam and may produce a convergingbeam, and the compressed beam may be formed by the converging beampassing through the collimating lens. In alternative embodiments, theimage compressor may have a concave reflective surface and a convexreflective surface and the concave reflective surface may receive theinput beam and may produce a converging beam, and the compressed beammay be formed by the converging beam reflecting off the concavereflective surface.

The image reformatter may have at least two reflective surfaces, whereone of the reflective surfaces may receive a portion of the compressedbeam and may reflect the portion for at least one reflection back andforth between the at least two reflective surfaces, wherein each of thesliced portions may be formed by a second portion of compressed beampassing by the at least two reflective surfaces after each of the atleast one reflection.

The image expander may comprise a concave lens and a convex lens,wherein the concave lens may receive the reformatted beam and mayproduce a diverging beam and the output beam may be produced by thediverging beam passing through the convex lens. In alternativeembodiments, the image expander may comprise a convex reflective surfaceand a concave reflective surface, wherein the convex reflective surfacemay receive the reformatted beam and may produce a diverging beam andthe output beam may be formed by the diverging beam reflecting off theconcave reflective surface.

In some embodiments of the present invention, the output spot may have alight intensity value that is substantially the same as the lightintensity of the input spot.

In another aspect of the present invention there is provided a method ofgenerating an output spot comprising the steps of compressing acollimated input beam, wherein the input beam, if passed through afocusing lens, produces an input spot; reformatting the compressed beaminto a plurality of sliced portions substantially vertically stacked andsubstantially parallel to each other; and expanding the reformatted beamto produce a collimated output beam which, when passed through afocusing lens, produces the output spot that is expanded in a firstdimension, and compressed in a second dimension, relative to the inputspot.

In some embodiments, the compressed beam may be compressed verticallyand may be substantially similar horizontally relative to the input beamand the output beam may be expanded horizontally relative to thereformatted beam and may have substantially similar dimensions to theinput beam.

In some embodiments, the number of sliced portions may be equal to aslicing factor, n, and the output spot may be expanded vertically by thefactor n and compressed horizontally by the factor n, relative to theinput spot.

In a further aspect of the present invention, an optical slicer having aslicing factor, n, is presented, the optical slicer comprising an imagecompressor which receives a substantially collimated input beam andcompresses the beam, wherein the collimated beam, if passed through afocusing lens, produces an input spot; an image reformatter whichreceives the compressed beam to reformat the beam into n sliced portionsof the compressed beam and vertically stacks the portions substantiallyparallel to each other; and an image expander which expands thereformatted beam to produce a collimated beam which, when passed throughthe focusing lens, produces an output spot compressed by the factor n ina first dimension relative to the input spot and expanded by the factorn in a second dimension relative to the input spot.

In another aspect of the present invention a multiplicative opticalslicer comprising a first optical slicer having a first slicing factor,m, and a second optical slicer having a second slicing factor, n, thefirst and second optical slicers being placed in series, and themultiplicative optical slicer having a slicing factor of m×n.

BRIEF DESCRIPTION OF FIGURES

For a better understanding of embodiments of the system and methodsdescribed herein, and to show more clearly how they may be carried intoeffect, reference will be made by way of example, to the accompanyingdrawings in which:

FIG. 1A shows a block diagram representation of an optical slicer havinga slicing factor of two;

FIG. 1B shows a block diagram representation of an optical slicer havinga slicing factor of four;

FIG. 2 shows an isometric view of an embodiment of an optical slicerhaving a slicing factor of two;

FIG. 3 shows an isometric view of an alternative embodiment of anoptical slicer having a slicing factor of two;

FIG. 4 shows an isometric view of an embodiment of an optical slicerhaving a slicing factor of four;

FIG. 5A shows an isometric view of an alternative embodiment of anoptical slicer having a slicing factor of four;

FIGS. 5B-5G shows isometric and plan views of embodiments of opticalelements of the optical slicer of FIG. 5A;

FIGS. 5H-5I shows an isometric view of an embodiment of a housing coverfor the optical slicer shown in FIG. 5A;

FIGS. 6A-6D show representations of alternative embodiments ofcompressors for use in an embodiment of an optical slicer; and

FIGS. 7A-7C show representations of alternative embodiments ofreformatters having a slicing factor of four for use in an embodiment ofan optical slicer.

DETAILED DESCRIPTION

It will be appreciated that for simplicity and clarity of illustration,where considered appropriate, reference numerals may be repeated amongthe figures to indicate corresponding or analogous elements or steps. Inaddition, numerous specific details are set forth in order to provide athorough understanding of the embodiments described herein. However, itwill be understood by those of ordinary skill in the art that theembodiments described herein may be practiced without these specificdetails. In other instances, well-known methods, procedures, andcomponents have not been described in detail so as not to obscure theembodiments described herein. Furthermore, this description is not to beconsidered as limiting the scope of the embodiments described herein inany way, but rather as merely describing the implementation of thevarious embodiments described herein.

With reference to FIG. 1A, a representation of optical slicer 100 isshown, optical slicer including image compressor 170, image reformatter172 and image expander 174. Optical slicer 100 receives input beam 102,as a collimated beam, which can be produced, for example by acollimating lens or a curved mirror. Input beam 102 also generates inputspot 180 when focused by a focusing lens having substantially the samefocal length as the collimating lens or curved mirror used to produceinput beam 102.

Image compressor 170 of optical slicer 100 receives input beam 102 andoutputs vertically compressed beam 114, anamorphically compressed in thevertical dimension, and having a smaller vertical dimension than and agreater horizontal dimension than that of input beam 102. Additionally,vertically compressed beam 114, if passed through a focusing lens withthe same focal length as the collimating lens or curved mirror used toproduce input beam 102 produces compressor spot 182, resulting in thefocusing of compressed beam 114 to project an image that issubstantially similar in the horizontal dimension as compared to inputspot 180, while being expanded in the vertical dimension.

In some embodiments, the image projected by vertically compressed beam114 may have the same horizontal width as input beam 102; however, thevertical height of vertically compressed light 114 may be compressed bythe slicing factor. The term “slicing factor” is used to describe thevalue of the horizontal compression and vertical expansion of the outputspot generated by the output beam of an optical slicer as compared tothe horizontal and vertical dimensions of the input spot generated bythe input beam into the optical slicer, the output and input spots beinggenerated when the output and input beams are each respectively focusedby the same focusing lens.

For example, for an optical slicer with a slicing factor of two, such asthe optical slicer represented in FIG. 1A, the output slicer producesoutput beam 156, which, if focused through a focusing lens having afocal length substantially equal to the focal length of the collimatinglens or convex minor that generated input beam 102, causes thegeneration of output spot 186. Focusing input beam 102 through the samefocusing lens will tend to generate input spot 180. Output spot 186having a vertical dimension that is twice that of input spot 180 and ahorizontal dimension that is half that of input spot 180. Thus, theslicing factor of the optical slicer produced by this configuration istwo.

In alternative embodiments, such as the representation of optical slicer100 shown in FIG. 1B, output spot 186 can similarly be generated byfocusing output beam 156 through a focusing lens having a focal lengthsubstantially equal to the focal length of the collimating lens orconvex minor that generated input beam 102. Focusing input beam 102through the same focusing lens generates input spot 180. In thisembodiment, output spot 186 has a vertical dimension that is four timesthat of input spot 180 and has a horizontal dimension that is ¼ that ofinput spot 180, thus, the slicing factor of optical slicer 100represented in FIG. 1B is four.

Other values of the slicing factor n are possible. The output spotgenerated by the output beam in a substantially similar manner asdiscussed above, may have a vertical dimension that is n times largerthan the vertical dimension of the input spot generated by the inputbeam and may tend to have a horizontal dimension that is 1/n of thehorizontal dimension of the input spot.

Referring back to FIG. 1A, vertically compressed beam 114 is received byimage reformatter 172 which outputs reformatted beams 136 and 138; suchreformatted formatted beams 136 and 138 being substantially verticallystacked and substantially parallel. Reformatted beams 136 and 138 aresliced portions of vertically compressed beam 114. In the embodimentshown, image reformatter 172 outputs two beam slices, which, in thisembodiment, is equal to the slicing factor of optical slicer 100;however, in some embodiments, image reformatter 172 may produce a numberof slices that is greater than or less than the slicing factor ofoptical slicer 100.

Each of reformatted beams 136 and 138, if passed through a focusing lenshaving the same focal length as the collimating lens or curved minorused to produce input beam 102, produces reformatter spot 184.Reformatter spot 184 is substantially the same dimension bothhorizontally and vertically, as compressor spot 182. Since reformattedbeams 136 and 138 are substantially vertically stacked and substantiallyparallel, the individual reformatter spots generated by each ofreformatted beams 136 and 138, combined to form reformatter spot 184,are projected atop one another, so as to double the light intensity ofreformatter spot 184 as compared to the individual reformatter spotsgenerated from each of beams 136 and 138 individually.

While the light intensity of reformatter spot 184 in the embodimentshown in FIG. 1A is double, as compared to the light intensity of eachindividual reformatter spot generated by each reformatted beam, in otherembodiments, the light intensity of reformatter spot 184, as compared tothe light intensity of each individual reformatter spot generated byeach reformatted beam, corresponds to the number of sliced portionsgenerated by image reformatter 174. For example, with reference to FIG.1B, optical slicer 100 is shown having image reformatter 172 thatproduces reformatted beams 136A, 136B, 138A and 138B, each of thereformatted beams being substantially parallel and substantiallyvertically stacked. Reformatted beams 136A, 136B, 138A and 138B aresliced portions of vertically compressed beam 114. Reformatter spot 184,generated by reformatted beams 136A, 136B, 138A and 138B in asubstantially similar manner as discussed above, has about four timesthe light intensity of each individual reformatter spot generated fromeach reformatted beam 136A, 136B, 138A and 138B.

With reference back to FIG. 1A, reformatted beams 136 and 138 arereceived by image expander 174 which expands reformatted beams 136 and138 by a factor of the slicing factor. In the embodiment shown, thereformatted beams 136 and 138 are expanded by a factor of two, in boththe horizontal and vertical directions (non-anamorphically), to produceoutput beam 156, output beam 156 which is made up of sliced beams 158and 160. Sliced beams 158 and 160 are expansions of reformatted beams136 and 138. Output beam 156 has substantially similar dimensions tothat of input beam 102. Projecting output beam 156 onto a lens, suchlens having substantially the same focal length as the collimating lensor curved mirror used to produce input beam 102, focuses output beam 156to produce output spot 186. Output spot 186 produces an image of inputspot 180 that can be compressed in the horizontal direction by theslicing factor and stretched in the vertical direction by the slicingfactor while maintaining a similar light intensity as input spot 180. Inembodiments, such as the embodiment represented in FIG. 1A, output spot186 can be two times larger in the vertical direction as input spot 180and can be compressed by two times in the horizontal direction as inputspot 180.

In other embodiments, such as the embodiment shown in FIG. 1B,reformatted beams 136A, 136B, 138A and 138B are received by imageexpander 174, which may be an anamorphic horizontal beam expander, toproduce output beam 156, made up of output slices 158A, 158B, 160A and160B, which are expansions of reformatted beams 136A, 136B, 138A and138B, expanded in the horizontal direction. In some embodiments, outputbeam 156 has similar dimensions as input beam 102. With respect to theembodiment represented by FIG. 1B, representing an optical slicer havinga slicing factor of four, when output beam 156 is projected onto a lenshaving substantially the same focal length as the collimating lens orcurved minor used to produce input beam 102, output beam 156 is focusedto produce output spot 186. Output spot 186 can be four times larger inthe vertical direction as input spot 180 and can be compressed by fourtimes in the horizontal direction as input spot 180, while maintaining asimilar light intensity as input spot 180.

It will be understood by those skilled in the art that the resultingoutput beam 156 of optical slicer 100, where optical slicer 100 has aslicing factor of n, when focused by a focusing lens havingsubstantially the same focal length as the collimating lens or curvedminor used to produce input beam 102, produces an output spot that is ntimes larger in the vertical direction and compressed by n times in thehorizontal direction, as compared to the input spot generated by inputbeam 102 passing through the same focusing lens, while maintaining asimilar light intensity as the input spot.

With reference to FIG. 2, optical slicer 100 is shown, including imagecompressor 170, image reformatter 172 and image expander 174. In FIG. 2,optical slicer 100 has a slicing factor of two. Input beam 102 can be asubstantially collimated beam, which can be produced by a collimatinglens or a curved minor. Input beam 102 generating an input spot whenfocused by a focusing lens having the same focal length as thecollimating lens or curved minor used to produce input beam 102.

Input beam 102 is received by image compressor 170 which outputsvertically compressed beam 114. Image compressor 170 has convexcylindrical lens 104 which receives input beam 102 and outputsvertically converging beam 108. Vertically converging beam 108 isreceived by concave cylindrical lens 110 which collimates verticallyconverging beam 108 and outputs vertically compressed beam 114. In otherembodiments, a pairing of multiple convex lenses can output verticallycompressed beam 114. In such alternative embodiments lens 104 can be aconvex lens and lens 108 can be a convex lens.

Additionally, vertically compressed beam 114, if passed through afocusing lens with the same focal length as the collimating lens orcurved mirror used to product input beam 102 produces a compressor spothaving a substantially similar dimension in the horizontal direction andexpanded in the vertical direction by a factor of the slicing factor ascompared to the input spot generated by passing input beam 102 throughthe same focusing lens. In the embodiment shown, the slicing factor istwo, when compared to the input spot generated by input beam 102 usingthe same focusing lens.

With reference to FIGS. 6A-6D, alternative embodiments of imagecompressor 170 are shown. Referring to FIG. 6A, image compressor 170 hascylindrical lens 602 which receives compressor input beam 600 andfocuses compressor input beam 600 for subsequent projection ontocollimating cylindrical lens 604 to produce an output beam that iscompressed relative to compressor input beam 600. In the embodimentshown in FIG. 6A, collimating cylindrical lens 604 is positioned beyondthe focal point of cylindrical lens 602, collimating cylindrical lens604 outputting an inverted image of compressor input beam 600 that iscompressed vertically.

With reference to FIG. 6B, image compressor 170 has an optical element612 having first surface 614 which focuses compressor input beam 600 inthe vertical direction and second surface 616 which substantiallycollimates the focused beam produced by first surface 614. The beamoutput from optical element 612 produces an output beam compressedvertically when compared with compressor input 600.

With reference to FIG. 6C, image compressor 170 has anamorphic prisms622 and 624, oriented such that compressor input beam 600 is refractedat the output face of each of anamorphic prisms 622 and 624. Theresulting output beam of image compressor 170 in this embodimentproduces an output beam compressed vertically when compared withcompressor input beam 600.

With reference to FIG. 6D, image compressor 170 has mirrors 632 and 634,compressor input beam 600 reflecting off concave surface of mirror 634and projecting onto convex surface of minor 632, to produce an outputbeam compressed vertically when compared with compressor input beam 600.

Skilled persons will understand that obvious variants of the compressorsdescribed herein, and obvious orientations of such compressors elementsmay be implemented to produce a beam that is compressed vertically ascompared to compressor input beam 600.

With reference back to FIG. 2, vertically compressed beam 114 isreceived by image reformatter 172 which outputs reformatted beams 136and 138, such reformatted beams 136 and 138 being substantially paralleland substantially vertically stacked. Image reformatter 172 includesside-by-side flat mirrors 116 and 118 and vertically stacked flatmirrors 128 and 130.

Side-by-side flat minors 116 and 118 can receive vertically compressedbeam 114, a portion of vertically compressed beam 114 being received byside-by-side flat mirror 116 and another portion of verticallycompressed beam 114 being received by side-by-side flat mirror 118,which slices vertically compressed beam 114 producing sliced beams 124and 126. Sliced beams 124 and 126 are reflected from side-by-side flatminors 116 and 118 onto vertically stacked minors 128 and 130, slicedbeam 124 being reflected onto vertically stacked mirror 128 and slicedbeam 126 being reflected onto vertically stacked mirror 130.

Sliced beams 124 and 126 are reflected off vertically stacked mirrors128 and 130 to produce reformatted beams 136 and 138. Reformatted beams136 and 138 are similar to sliced beams 124 and 126 but aresubstantially vertically stacked and substantially parallel. In someembodiments, vertically stacked minors 128 and 130 are D-shaped minorsand can be optically flat and fully aluminized, or mirrorized, to within50 μm of their adjacent edges; however, a skilled person will understandthat other reflective properties may achieve substantially similarresults.

If reformatted beams 136 and 138 are passed through a focusing lens withthe same focal length as the collimating lens or curved minor used toproduce input beam 102, a reformatter spot is produced. In theembodiment shown, this reformatter spot has the same horizontaldimension and a vertical dimension which is four times that of the inputspot formed by passing input beam 102 through the same focusing lens,while maintaining a similar light intensity as the input spot.

With reference to FIGS. 7A-7C, alternative embodiments of imagereformatter 172 are shown. Referring to FIG. 7A, image reformatter 172has multiple pairs of mirrors each to receive a portion of reformatterinput beam 700 and each positioned to produce a portion of reformattedbeam 720, reformatted beam 720 being made up of beam portions 720A,720B, 720C and 720D, each beam portion being substantially parallel andsubstantially vertically stacked and being a sliced portion inreformatter input beam 700. Minor pairs 702 and 712 can receive a firstportion of reformatter input beam 700, the first portion reflecting offminor 702 and received by mirror 712, mirror 712 being aligned toproduce beam portion 720D. Mirror pairs 704 and 714 receive a secondportion of reformatter input beam 700, the second portion reflecting offmirror 704 and received by minor 714, minor 714 being aligned to producebeam portion 720C. Mirror pairs 706 and 716 receive a third portion ofreformatter input beam 700, the third portion reflecting off minor 706and received by mirror 716, minor 716 being aligned to produce beamportion 720B. Minor pairs 708 and 718 receive a fourth portion ofreformatter input beam 700, the fourth portion reflecting off mirror 708and received by minor 718, minor 718 being aligned to produce beamportion 720A. A skilled person will appreciate that the addition ofadditional minor pairs can increase the number of beam portions ofreformatted beam 720.

Referring to FIG. 7B, image reformatter 172 includes reflective surfaces730 and 732. When in use, reformatter input 700 is received byreflective surface 730 and can be reflected back and forth betweenreflective surface 732, a portion of the reflected beam being reflectedoff reflective surface 732 and passing by reflective surface 730 toproduce a beam portion of output beam 720 until each of beam portions720A, 720B, 720C and 720D are generated, each beam portion beingsubstantially parallel and substantially vertically stacked relative toone another and each being a sliced portion of reformatter input 700. Askilled person will appreciate that additional beam portions may begenerated by adjusting the position of reflective surfaces 730 and 732to produce additional reflections back and forth between reflectivesurfaces 730 and 732, each of the reflections continuing to provide fora portion of the reflected beam to pass by reflective surface 730 toform a beam portion of output beam 730.

Referring to FIG. 7C, image reformatter 172 may be comprised of twostages, a first stage being comprised of reflective surfaces 740 and 742and a second stage being comprised of reflective surfaces 744 and 746. Aportion of reformatter input 700 passing by reflective surface 740,producing beam portion 750B of first output beam 750, and a secondportion of input beam may be reflected off reflective surface 740 ontoreflective surface 742 to form beam portion 750A of first output beam750 which tends to pass by reflective surface 740. Each of beam portions750A and 750B being substantially parallel and substantially verticallystacked. Beam 750 may then partially be received by reflective surface744, a portion of beam 750 passing by reflective surface 744 to produceoutput beams 720C and 720D, the remaining portion of beam 750 beingreflected off reflective surface 744 onto reflective surface 746. Thereflection of the beam portion off reflective surface 746 producingoutput beam portions 720A and 720B of output beam 720, which can pass byreflective surface 744. Beam portions 720A, 720B, 720C and 720D beingsubstantially vertically stacked and substantially parallel and beingsliced portions of reformatter input 700. A skilled person willappreciate that by adding additional stages, output beam can be made upof additional beam portions. For example, adding an additional stage mayproduce eight beam portions, and a further stage producing sixteen beamportions.

Referring back to FIG. 2, reformatted beams 136 and 138 are received byimage expander 174 producing output beam 156, output beam 156 being madeup of sliced beams 158 and 160. Image expander 174 has concave lens 142which can receive reformatted beams 136 and 138, and can uniformlyexpand reformatted beams 136 and 138 producing expanding beam 146. Imageexpander 174 can additionally have collimating lens 148 which receivesexpanding beam 146 and substantially collimates expanding beam 146,producing output beam 156. In some embodiments, concave lens 142 andcollimating lens 148 may be cylindrical lenses which can expandreformatted beams 136 and 138 horizontally, while maintaining theirvertical dimension.

Passing output beam 156 through a focusing lens having substantially thesame focal length as the collimating lens or curved mirror used toproduce input beam 102, focuses output beam 156 to produce an outputspot. This output spot can project an image of the input spot generatedby passing input beam 102 through the same focusing lens, the outputspot being compressed in the horizontal direction by the slicing factorand expanded in the vertical direction by the slicing factor, whilemaintaining a light intensity that is similar to the light intensity ofthe input spot generated by input beam 102 passing through the samefocusing lens. In the embodiment of optical slicer 100 shown in FIG. 2,the output spot generated by output beam 156 is two times larger in thevertical direction and compressed by two times in the horizontaldirection, compared to the input spot generated by passing input beam102 through the same focusing lens.

With reference to FIGS. 6A-6D, a skilled person would appreciate thatthe various alternative embodiments of the compressor shown in FIGS.6A-6D can be used as expanders as well, if such embodiments areimplemented with the light beams being projected in the oppositedirection as the light beams shown in FIGS. 6A-6D. Additionally, skilledpersons will appreciate that other apparatus comprising of opticalelements can be implemented and positioned appropriately to produceexpanded beam 156.

With reference to FIG. 3, an embodiment of optical slicer 100 is shown.Optical slicer 100 having image compressor 170, image reformatter 172and image expander 174. In the embodiment shown in FIG. 3, opticalslicer has a slicing factor of two. Image compressor 170, havingconverging lens 302, reflective surfaces 304 and 306 and collimatinglens 310, receives an input beam at converging lens 302, producing aconverging beam, being received and reflected by reflective surface 304to reflective surface 306. The converging beam reflecting off reflectivesurface 306 where it passes through collimating lens 310, substantiallycollimating the beam, and directing the collimated beam to imagereformatter 172

Image reformatter has reflective surfaces 312 and 316, each ofreflective surfaces 312 and 316 being connected to mounting brackets 314and 318 respectively, for securement to housing 320 of optical slicer100. Reflective surfaces 312 and 316 can be D-shaped minors andreflective surface 312 can be oriented vertically, with the flat edgebeing the closest edge to the reformatted beam output by reformatter andreflective surface 316 oriented with the curved edge facing downwards.

The compressed beam output from compressor 170 passes by reflectivesurface 312 and a portion of the compressed beam passes by reflectivesurface 316, the remaining portion of the compressed beam reflecting offreflective surface 312 back towards reflective surface 316. This firstbeam portion of the compressed beam passing by both reflective surfacesforming a first portion of the reformatted beam output by imagereformatter 172. The remaining portion of the compressed beam reflectingback towards reflective surface 316, and reflecting back and forthbetween reflective surfaces 316 and 312 each time a portion of thereflected compressed beam passing by reflective surface 312 forming asubsequent beam portion of reformatted beam. The portions of reformattedbeam being substantially vertically stacked and substantially parallel,and each representing a sliced portion of the compressed beam.

Image reformatter 172 in the embodiment shown in FIG. 3 forming areformatted beam made up of two beam portions, the two portionssubstantially parallel and substantially vertically stacked and eachrepresenting a portion of the compressed beam output from imagecompressor 170. A first portion of the compressed beam reflecting offreflective surface 312 and back towards reflective surface 316, thisportion subsequently being reflected off reflective surface 316 andpassing by reflective surface 316, resulting in the reformatted beamhaving two portions. Skilled persons will understand that an increase inthe number of back and forth reflections between reflective surfaces 316and 312 can increased the number of portions of the reformatted beam.

Image expander 174, in the embodiment shown in FIG. 3, receives thereformatted beam from image reformatter 172 and produces an expandedcollimated output beam, the expanded collimated output beam being ofsimilar dimensions as the input beam directed into optical slicer 100.Image expander 174, in the embodiment shown in FIG. 3, can be comprisedof appropriate lenses and/or mirrors, to expand and collimatereformatted beam appropriately.

The resulting output beam, when passed through a focusing lens havingsubstantially the same focal length as the collimating lens or curvedminor that generated the collimated input beam, focuses the output beamto produce an output spot. This output spot producing an image of theinput spot that would be generated if the input beam were passed throughthe same focusing lens being compressed in the horizontal direction bythe slicing factor of optical slicer 100 and expanded in the verticaldirection by the slicing factor of optical slicer 100, while maintaininga similar light intensity as the input spot generated by the input beamwhen passed through the same focusing lens. The output spot generated bythe output beam of optical slicer 100 shown in FIG. 3 being two timescompressed in the horizontal direction and expanded by two times in thevertical direction, optical slicer 100 shown in FIG. 3 being an opticalslicer having a slicing factor of two.

With reference to FIG. 4, optical slicer 100 is shown having imagecompressor 170, image reformatter 172 and image expander 174. In theembodiment shown in FIG. 4, optical slicer 100 has a slicing factor offour. Input beam 102 can be substantially collimated, which can beproduced by a collimating lens or a curved mirror.

Input beam 102 is received by image compressor 170 can output compressedbeam 452. Image compressor 170 having cylindrical concave mirror 402which reflects input beam 102 to generate vertically converging beam450.

With additional reference to FIGS. 5A and 5B, cylindrical concave mirror402 can be mounted to mounting bracket 502 for securement to base plate480 of optical slicer 100. In some embodiments, cylindrical concaveminor 402 may have a focal length of 103.360 mm and can be positioned ata 7.3 degree tilt horizontally and a 0.0 degree tilt vertically relativeto the path of the incoming beam; however skilled persons willunderstand that other focal lengths and positioning can be used toproduce vertically converging beam 450.

Vertically converging beam 450 may be received by cylindrical convexmirror 404 which collimates vertically converging beam 450 outputtingcompressed beam 452. With additional reference to FIGS. 5A and 5C,cylindrical convex mirror 404 can be mounted to mounting bracket 504 forsecurement to base plate 480 of optical slicer 100. In some embodiments,cylindrical convex mirror 404 can have a focal length of −25.84 mm andmay be positioned at a 7.3 degree tilt horizontally and a 0.0 degreetilt vertically relative to the path of the incoming beam; however,skilled persons will understand that other focal lengths and positioningcan be used to produce compressed beam 452.

In some embodiments, compressed beam 452, if passed through a focusinglens with the same focal length as the collimating lens or curved mirrorused to produce input beam 102, produces a compressor spot that isexpanded in the vertical direction by the slicing factor and having asimilar horizontal dimension when compared to the input spot generatedby passing input source 102 through the same focusing lens.

With reference back to FIG. 4, compressed beam 452 is received by imagereformatter 172 which outputs reformatted beam 456, reformatted beam 456being made up of portions 456A, 456B, 456C and 456D each beingsubstantially parallel and substantially vertically stacked, and eachbeing a sliced portion of compressed beam 452.

With additional reference to FIGS. 5A, 5D and 5E, image reformatter 172can have D-shaped mirrors 406 and 410. D-shaped minor 406 can be mountedto mounting bracket 408, and can be secured to bracket 420, bracket 420secured to base plate 480 of optical slicer 100. D-shaped minor 406 canbe vertically oriented with the flat edge being located closest toreformatted beam 456 when in use. D-shaped minor 406 can be positionedat a 2.5 degree tilt horizontally and a 2.7 degree tilt verticallydownwards relative to the incoming path of compressed beam 452, whencompressed beam 452 first approaches D-shaped mirror 406.

D-shaped mirror 410 can be mounted to mounting bracket 412, which can besecured to bracket 422, bracket 422 being secured to base plate 480 ofoptical slicer 100. D-shaped minor 410 can be oriented horizontally withthe flat edge being located closest to reformatted beam 456 when in use.D-shaped minor 410 can be positioned at a 2.5 degree tilt horizontallyand a 2.7 degree tilt vertically upwards relative to the incoming pathof compressed beam 452, when compressed beam 452 first approachesD-shaped mirror 406. In some embodiments, D-shaped mirrors 406 and 410may be Thorlabs™ #BBD1-E02 mirrors. Skilled persons will understand thatdifferently shaped mirrors or other reflective surfaces, includingconvex or concave shaped surfaces can be used to produce reformattedbeam 456, and additionally, alternative positioning of minors or otherreflective surfaces may be implements to achieve substantially similarresults.

When in use, compressed beam 452 can pass over D-shaped mirror 410 andcan reach the position of D-shaped mirror 406. In some embodiments,portion 456A of compressed beam 452 passes by D-shaped mirror 406, whilethe remaining portion of compressed beam 452 is reflected back and forthbetween D-shaped mirror 406 and D-shaped mirror 410 until reformattedbeam 456, made up of portions 456A, 456B, 456C and 456D is generated.With each reflection back and forth a portion of the reflected beampasses by D-shaped mirror 406 to produce a corresponding portion ofreformatted beam 456. For example, after portion 456A has passed byD-shaped minor 406, the remaining portion of compressed beam 452 isreflected off D-shaped mirror 406, generating a first reflected beamdirected toward at D-shaped minor 410.

D-shaped mirror 410 reflects the first reflected beam back towardsD-shaped minor 406, a portion of this reflection passing by D-shapedmirror 406, generating portion 456B, the remaining portion of thisreflection be directed back at D-shaped minor 410. Portion 456B beingpositioned below portion 456A, and being substantially parallel toportion 456A and substantially vertically stacked.

The remaining portion of the reflection directed at D-shaped minor 406,generating a subsequent reflected portion, directed back to D-shapedminor 410. This subsequent reflected portion contacting D-shaped minor410 at a position below the contact position of the first reflectedportion. This subsequent reflected portion reflecting off D-shaped minor410 back towards D-shaped minor 406, a portion passing by D-shapedmirror 406, generating portion 456C, the remaining portion of thereflected beam contacting D-shaped minor 406. Portion 456C beingpositioned below portion 456B, each of portions 456A, 456B and 456Cbeing substantially parallel and substantially vertically stacked.

Again, the remaining portion of the reflection is directed at D-shapedminor 406, generating a further reflected portion, directed back toD-shaped minor 410. This further reflected portion contacts D-shapedminor 410 at a position below the contact position of the previousreflected portion. This further reflected portion reflects off D-shapedminor 410 and passes by D-shaped mirror 406, generating portion 456D.Portion 456D is positioned below portion 456C, each of portions 456A,456B, 456C and 456D being substantially parallel and substantiallyvertically stacked and each being a sliced portion of compressed beam452.

While the embodiment shown in FIG. 4 is an optical slicer that generatesfour beam portions, a person of skill will understand that an increasein the number of back and forth reflections between D-shaped mirrors 406and 410 can increased the number of portions of reformatted beam 456.Skilled persons will appreciate that the focal lengths and sizes ofminors 402, 404, 414 and 416 may be adjusted appropriately toaccommodate such modifications.

Referring back to FIG. 4, if reformatted beam 456 is passed through afocusing lens with the same focal length as the collimating lens orcurved mirror used to produce input beam 102, a reformatter spot isproduced. The produced reformatter spot producing an image of input beam102, that is expanded in the vertical dimension by the slicing factorand has a similar horizontal dimension as compared to the input spotgenerated by passing input beam 102 through the same focusing lens,while maintaining a similar light intensity as the input spot.

Reformatting beam 456 may be received by image expander 174, producingoutput beam 156. Image expander 174 having cylindrical convex minor 414and cylindrical concave minor 416. Cylindrical convex mirror 414receiving and reflecting reformatted beam 456, producing horizontallydiverging reformatted beam 458 directed at cylindrical concave minor416. Cylindrical concave minor 416 receiving horizontally divergingreformatted beam 458 and substantially collimating horizontallydiverging reformatted beam 458, producing output beam 156. Withadditional reference to FIG. 5A, output beam 156 passes through outputaperture 520, which can be located below cylindrical convex mirror 414and through mounting bracket 514.

The resulting output beam 156, if passed through a focusing lens havingsubstantially the same focal length as the collimating lens or curvedmirror that generated the input beam 102, focuses output beam 156 toproduce an output spot. This output spot producing an image of the inputspot that would be generated if input beam 102 is passed through thesame focusing lens but being compressed in the horizontal direction bythe slicing factor of optical slicer 100 and expanded in the verticaldirection by the slicing factor of optical slicer 100, while maintaininga similar light intensity as the input spot.

With additional reference to FIGS. 5A and 5F, cylindrical convex mirror414 can be secured to mounting bracket 514 for securement to base plate480 of optical slicer 100. In some embodiments, mounting bracket 514 canhave output aperture 520 located therethrough, where in some embodimentsoutput aperture 520 can be located below the position of cylindricalconvex minor 414 when secured to mounting bracket 514. In someembodiments, cylindrical convex minor 414 may have a focal length of−25.84 mm and may be positioned at a 0.0 degree tilt horizontally and a6.3 degree tilt vertically downwards relative to the path of theincoming beam; however, skilled persons will understand that other focallengths and positioning can be used to produce horizontally divergingreformatted beam 458.

With additional reference to FIGS. 5A and 5G, cylindrical concave minor416 can be mounted to mounting bracket 516 for securement to base plate480 of optical slicer 100. In some embodiments, base plate 480 having anindent therein which can receive a portion of mounting bracket 516 toprovide that a portion of concave mirror 416 can rest below a topsurface of base plate 480. In some embodiments, cylindrical concaveminor 416 can have a focal length of 103.360 mm and can be positioned ata 0.0 degree tilt horizontally and a 6.3 degree tilt vertically upwardsrelative to the path of the incoming beam; however, skilled persons willunderstand that other focal lengths and positioning can be used toproduce output beam 156.

With reference to FIG. 5H, optical slicer 100 can be covered by housingcover 486 secured to base plate 480 to protect the interior elements ofoptical slicer 100, for example from dust and other particulates.Housing cover 486 can have input aperture 482 for receiving the inputbeam and can additionally have output aperture 484 for outputting theoutput beam from optical slicer 100.

In some embodiments of the optical slicer described herein, a secondoptical slicer may be placed in series wherein output beam 156 from afirst optical slicer may be input beam 102 into a second optical slicer.In such embodiments it has been found that the slicing factor may bemultiplicative; for example, combining two slicers having a slicingfactor of four in series may tend to result in an overall slicing factorof sixteen.

While the present invention can be used with any device that tends touse light as an input, one example of the use of the optical slicerdescribed herein may be in the field of spectroscopy. A generalspectrometer is a device that disperses light such that the intensityvalue of light as a function of wavelength can be recorded on adetector. For readings that require a higher spectral resolution, anarrower slit is needed in a direct relationship to spectral resolutionand typically, a narrow slit will provide a reduction in the lightintensity received by the general spectrometer device. Positioning anoptical slicer in front of the input of a general spectrometer devicecan tend to produce an input into the general spectrometer device slithaving an increased light intensity value as compared to a slit withoutan optical slicer, by the factor of the slicing factor, over the area ofthe slit, tending to provide increased spectral resolution withoutsacrificing light signal intensity.

A subset of spectroscopy is interferometric spectroscopy; the definingfeature of interferometric spectrometers is that the dispersing elementused is not a grating or a prism. Rather, the dispersion is achievedanother way, such as by taking the Fourier transform of the patterngenerated by two interfering beams. The slicer not only increasesbrightness of the output, but also allows large improvements in thecontrast of the interference fringes, as well as signal-to-noise ratio.

An optical slicer can be used in a subset of OCT called Fourier domainOCT (FD-OCT), and more specifically in a specific implementation FD-OCTcalled Spectral Domain OCT (SD-OCT). An SD-OCT instrument is aninterferometric spectrometer with a dispersive spectrometer to recordthe signal. An optical slicer can be included at the input to thedispersive spectrometer right before the dispersive beam element in acollimated beam path.

A further subset of interferometric spectrometry as pertains to medicalimaging is Optical Coherence Tomography (OCT), a technique that uses aninterferometric spectrometer to make an image. A slicer will improve thethroughput, as well as the fringe contrast, of the OCT device; theresult is that the slicer can improve the depth penetration possiblewith OCT systems, speeding imaging time and increasing the value of thecaptured image. An optical slicer can be included at the input to theOCT device.

A further application of the slicer is in the field of miniaturespectroscopy, particularly as it pertains to Raman spectroscopy. CurrentRaman spectrometers have been implemented that are miniaturized tohandheld scale. As the slicer can be used to increase throughput in anysystem wherein light is used as the input source, a miniaturizedembodiment of the slicer can be used in conjunction with miniaturizedspectrometers, like the Raman, to increase spectral resolution, increaseoutput signal strength, and decrease scan time. An optical slicer can beincluded at the input to the Raman spectroscopy device.

The present invention has been described with regard to specificembodiments. However, it will be obvious to persons skilled in the artthat a number of variants and modifications can be made withoutdeparting from the scope of the invention as described herein.

1. An optical slicer for generating an output spot comprising: a beam compressor which receives a substantially collimated input beam and compresses the beam; a beam reformatter which receives the compressed beam to reformat the beam into a plurality of sliced portions of the compressed beam and vertically stacks the portions substantially parallel to each other; and a beam expander which expands the reformatted beam to produce a collimated output beam for producing the output spot that is expanded in a first dimension and compressed in a second dimension relative to an input spot produced from the input beam.
 2. The optical slicer of claim 1, wherein the compressed beam is compressed vertically and is substantially similar horizontally relative to the input beam.
 3. The optical slicer of claim 2, wherein the output beam is expanded horizontally relative to the reformatted beam and has substantially similar dimensions to the input beam.
 4. The optical slicer of claim 3, wherein the number of sliced portions of the compressed beam is equal to a slicing factor, n.
 5. The optical slicer of claim 4, wherein the output spot is expanded vertically by the factor n and compressed horizontally by the factor n.
 6. The optical slicer of claim 3, wherein the beam compressor comprises a convex lens and a concave lens, wherein the convex lens receives the input beam and produces a converging beam and the compressed beam is formed by the converging beam passing through the concave lens.
 7. The optical slicer of claim 3, wherein the beam compressor comprises a concave reflective surface and a convex reflective surface, wherein the concave reflective surface receives the input beam and produces a converging beam and the compressed beam is formed by the converging beam reflecting off the convex reflective surface.
 8. The optical slicer of claim 3, wherein the beam reformatter comprises at least two reflective surfaces, wherein one of the reflective surfaces receives a portion of the compressed beam and reflects the portion for at least one reflection back and forth between the at least two reflective surfaces, and wherein each of the sliced portions is formed by a second portion of compressed beam passing by the at least two reflective surfaces after each of the at least one reflection.
 9. The optical slicer of claim 3, wherein the beam expander comprises a concave lens and a convex lens, and wherein the concave lens receives the reformatted beam and produces a diverging beam and the output beam is produced by the diverging beam passing through the convex lens.
 10. The optical slicer of claim 3, wherein the beam expander comprises a convex reflective surface and a concave reflective surface, and wherein the convex reflective surface receives the reformatted beam and produces a diverging beam and the output beam is formed by the diverging beam reflecting off the concave reflective surface.
 11. The optical slicer of claim 3, where the output spot has a light intensity substantially the same as the light intensity of the input spot.
 12. A spectrometer comprising the optical slicer of any of claims 1 to 11, wherein the slicer is positioned upstream of the optical input slit of the spectrometer to direct the output spot therethrough.
 13. A method of generating an output spot comprising: compressing a collimated input beam; reformatting the compressed beam into a plurality of sliced portions substantially vertically stacked and substantially parallel to each other; and expanding the reformatted beam to produce a collimated output beam for producing an output spot that is expanded in a first dimension and compressed in a second dimension relative to an input spot produced from the input beam.
 14. The method of claim 13, wherein the compressed beam is compressed vertically and is substantially similar horizontally relative to the input beam.
 15. The method of claim 14, wherein the output beam is expanded horizontally relative to the reformatted beam and has substantially similar dimensions to the input beam.
 16. The method of claim 15, wherein the number of sliced portions is equal to a slicing factor, n.
 17. The method of claim 16, wherein the output spot is expanded vertically and compressed horizontally by the factor n. 